1. Field of the Invention
The present invention relates to new catalysts for the production of olefinic hydrocarbons by oxidative dehydrogenation and to methods of using the same. More particularly, this invention relates to tungsten-based catalysts for the oxidative dehydrogenation of hydrocarbons to yield olefins, and preferably, to the production of light olefins from light hydrocarbons.
2. Description of the Related Art
Several publications are referenced in this application. These references describe the state of the art to which this invention pertains, and are incorporated herein by reference.
Olefinic hydrocarbons, such as ethylene, propene, butene, and isobutene, are critical intermediates in the petrochemical industry. In order to satisfy market demand, substantial efforts have been invested in the production of such compounds by conventional catalytic dehydrogenation methods. For example, U.S. Pat. No. 5,468,710 to Resasco et al. describes the use of a composition containing sulfided nickel and non-acidic alumina as a catalyst for conventional dehydrogenation of organic compounds, such as isobutane, to yield the corresponding olefin.
However, conventional dehydrogenation has several disadvantages, including the need for high reaction temperatures (e.g., 550-650° C.), the deactivation of the catalyst by coke formation, and the consequent need for periodic catalyst regeneration at 20-30 minute intervals throughout the process. In addition, there are thermodynamic limitations on the activity of catalysts for conventional dehydrogenation. For example, such catalysts are only 85% selective at 45-50% isobutane conversion.
As a result of these substantial drawbacks, the petroleum industry has sought a solution to the demand for olefinic hydrocarbons in the use of oxidative dehydrogenation methods. Oxidative dehydrogenation is not subject to the problems associated with conventional dehydrogenation because of the presence of oxygen in the reaction mixture. However, to date, no commercial catalyst systems are available for oxidative dehydrogenation methods.
Various methods have been used to develop such a catalyst system. For example, U.S. Pat. Nos. 3,821,324; 3,933,933; and 4,164,519 describe oxidative dehydrogenation catalysts comprising titanium, at least one component selected from tungsten and molybdenum, and at least one additional component selected from phosphorus, bismuth, lead, antimony, and arsenic.
Japanese Patent Publication No. JP 07010782 describes the uses of an oxidative dehydrogenation catalyst to prepare isobutene and methacrolein. The catalyst contained molybdenum, iron, cobalt, cesium, silicon, bismuth, phosphorus, and nitrogen. A mixture of isobutane, oxygen, and nitrogen gas was passed through a reactor containing the mixed oxide catalyst at 440° C. to yield the corresponding olefins, isobutene, propene, and methacrolein, at a 3.8% conversion, with 13.9, 3.3, and 18.9% selectively, respectively. Similarly, Japanese Patent Publication No. JP 93150371 describes the use of alkali metal- and alkaline earth metal-containing catalysts for the preparation of isobutene and methacrolein from isobutane. The oxidative dehydrogenation catalysts and mixed oxide catalysts contained bismuth and molybdenum.
Japanese patent 3-218327 describes the oxidative dehydrogenation of propane or isobutane using a catalyst comprising either tin oxide and phosphorous oxide as the main components, or indium oxide and phosphorous oxide as the main components. However, the selectivity was only 32% at 1.4% conversion. Similarly, U.S. Pat. No. 5,759,946 describes a catalyst based on chromium oxide for oxidative dehydrogenation of hydrocarbons, and European Patent Publication No. EP 0557790 discloses the use of a catalyst containing phosphorous oxide for producing isobutene by oxidative dehydrogenation of isobutane. However, like the catalysts described above, these catalysts suffer from low selectivity and/or yield.
D. Stem and R. K. Grasselli (J. Catal., Volume 167, pages 570-572 (1997)) disclose the use of several metal tungstate catalysts containing cobalt, nickel, iron, zinc, and cerium for the oxidative dehydrogenation of propane. A maximum yield of 9.1% was obtained using cobalt tungstate catalyst at a selectivity of 65.1% and at a reaction temperature of 560° C.
Sodium tungstate in combination with hydrogen peroxide was used as a catalyst for the epoxidation of unsaturated aldehydes and carboxylic acids (see EP 434546 and Ballisteri et al., Stud. Org. Chem., Volume 33, pages 341-46 (1988)). This catalyst was also used for the epoxidation of a cyclohexene ring in various organic compounds (see also Japanese Patent Publication JP 62230778). However, to date, tungsten-based catalysts have not been used for olefin production by oxidative dehydrogenation of hydrocarbons at reasonably high selectivity.
In view of the foregoing, it is evident that the art has not succeeded in achieving high conversion at high selectivity, such that the yield of the desired olefin is maximized, as extraneous oxidative side reactions are minimized. None of the prior art references disclose or suggest tungsten-based catalysts which provide selective production of olefins from hydrocarbons by oxidative dehydrogenation. Accordingly, it would be desirable to produce a new catalyst for use in the selective production of olefins from hydrocarbons by oxidative dehydrogenation.